;(function(win, lib) {
   var doc = win.document;
   var docEl = doc.documentElement;
   var metaEl = doc.querySelector('meta[name="viewport"]');
   var flexibleEl = doc.querySelector('meta[name="flexible"]');
   var dpr = 0;
   var scale = 0;
   var tid;
   var flexible = lib.flexible || (lib.flexible = {});
   
   if (metaEl) {
       // console.warn('将根据已有的meta标签来设置缩放比例');
       var match = metaEl.getAttribute('content').match(/initial\-scale=([\d\.]+)/);
       if (match) {
           scale = parseFloat(match[1]);
           dpr = parseInt(1 / scale);
       }
   } else if (flexibleEl) {
       var content = flexibleEl.getAttribute('content');
       if (content) {
           var initialDpr = content.match(/initial\-dpr=([\d\.]+)/);
           var maximumDpr = content.match(/maximum\-dpr=([\d\.]+)/);
           if (initialDpr) {
               dpr = parseFloat(initialDpr[1]);
               scale = parseFloat((1 / dpr).toFixed(2));    
           }
           if (maximumDpr) {
               dpr = parseFloat(maximumDpr[1]);
               scale = parseFloat((1 / dpr).toFixed(2));    
           }
       }
   }

   if (!dpr && !scale) {
       var isAndroid = win.navigator.appVersion.match(/android/gi);
       var isIPhone = win.navigator.appVersion.match(/iphone/gi);
       var devicePixelRatio = win.devicePixelRatio;
       if (isIPhone) {
           // iOS下，对于2和3的屏，用2倍的方案，其余的用1倍方案
           if (devicePixelRatio >= 3 && (!dpr || dpr >= 3)) {                
               dpr = 3;
           } else if (devicePixelRatio >= 2 && (!dpr || dpr >= 2)){
               dpr = 2;
           } else {
               dpr = 1;
           }
       } else {
           // 其他设备下，仍旧使用1倍的方案
           dpr = 1;
       }
       scale = 1 / dpr;
   }

   docEl.setAttribute('data-dpr', dpr);
   if (!metaEl) {
       metaEl = doc.createElement('meta');
       metaEl.setAttribute('name', 'viewport');
       metaEl.setAttribute('content', 'initial-scale=' + scale + ', maximum-scale=' + scale + ', minimum-scale=' + scale + ', user-scalable=no');
       if (docEl.firstElementChild) {
           docEl.firstElementChild.appendChild(metaEl);
       } else {
           var wrap = doc.createElement('div');
           wrap.appendChild(metaEl);
           doc.write(wrap.innerHTML);
       }
   }

   function refreshRem(){
       var width = docEl.getBoundingClientRect().width;
       if (width / dpr > 540) {
           width = 540 * dpr;
       }
       var rem = width / 10;
       docEl.style.fontSize = rem + 'px';
       flexible.rem = win.rem = rem;
   }

   win.addEventListener('resize', function() {
       clearTimeout(tid);
       tid = setTimeout(refreshRem, 300);
   }, false);
   win.addEventListener('pageshow', function(e) {
       if (e.persisted) {
           clearTimeout(tid);
           tid = setTimeout(refreshRem, 300);
       }
   }, false);

   if (doc.readyState === 'complete') {
       doc.body.style.fontSize = 12 * dpr + 'px';
   } else {
       doc.addEventListener('DOMContentLoaded', function(e) {
           doc.body.style.fontSize = 12 * dpr + 'px';
       }, false);
   }
   

   refreshRem();

   flexible.dpr = win.dpr = dpr;
   flexible.refreshRem = refreshRem;
   flexible.rem2px = function(d) {
       var val = parseFloat(d) * this.rem;
       if (typeof d === 'string' && d.match(/rem$/)) {
           val += 'px';
       }
       return val;
   }
   flexible.px2rem = function(d) {
       var val = parseFloat(d) / this.rem;
       if (typeof d === 'string' && d.match(/px$/)) {
           val += 'rem';
       }
       return val;
   }

})(window, window['lib'] || (window['lib'] = {}));